The long-range goals of this proposed study are to: define essential structural and functional regulatory mechanisms of spermatogenesis, determine intratesticular events responsible for reduced fertility as evidenced in varicocele and determine a more discrete etiology of the subfertility associated with varicocele. Testicular tissue, testicular venous blood and semen will be collected and studied from rabbits with surgically induced varicocele and again from these rabbits following repair of the varicocele. Our approach utilizing the varicocele model (control, varicocele and varicocele repaired rabbits) is to correlate data derived from ultrastructural studies of testicular tissue with data from endocrine and biochemical studies of testicular venous blood and biochemical and kinetic studies of semen. It is expected that this study will provide a clear definition of spermatogenic defects which result in the failure of normal germ cell development as illustrated in varicocele, identify structural and functional mechanisms of spermatogenic disruption perhaps common to this and other testicular disorders, more clearly define the tiology of varicocele-induced subfertility, and lead to both diagnostic and prognostic determinants concerning the role of varicocele in infertility.